Why Do Drunk People Stumble, Fumble, and Slur Their Words?

Alcohol causes Purkinje neurons in the cerebellum to become discombobulated.

One of the first signs of being drunk is a lack of bodily coordination that includes the inability to articulate words. A drunk person will stereotypically stumble, fumble, and slur his or her words. What does alcohol do to the brain that causes this loss of motor control? Recently, neuroscientists have identified specific neurons in the cerebellum that are at the root of alcohol's discombobulating effects.

The May 2015 study, "'Simulation of Alcohol Action Upon a Detailed Purkinje Neuron Model and a Simpler Surrogate Model that Runs >400 Times Faster," was published in the journal BMC Neuroscience.

Although the cerebellum is only 10% of brain volume it holds over 50% of your brain's total neurons. As a neuroscientist, my father was always perplexed and intrigued by this disproportionate distribution of neurons. He would often say, "We don't know exactly what the cerebellum is doing, but whatever it's doing, it's doing a lot of it."

Traditionally, neuroscience credits the cerebellum with being responsible for the relatively simple tasks of coordinating muscle movements, maintaining balance, posture, and proprioception (tracking your body's position in space).

Until recently, neuroscientists haven't given the cerebellum much credit for higher executive functions, cognition, psychiatric disorders, or emotional regulation. Luckily, this outdated viewpoint about the cerebellum is rapidly evolving.

My dad was obsessed with the cerebellum and passed this obsession on to me. Over the years, I've written extensively about the everchanging views on the role our cerebellum plays in brain function and performance both on and off the court.

On a scale of -5 to +5, alcohol takes someone "south of zero" in terms of having a highly functioning cerebellum. On the flip side, regular practice enhances cerebellar (of or pertaining to the cerebellum) function and takes someone "north of zero" when performing any sport, playing a musical intstrument, or performing any skill that requires muscular coordination.

As an athlete, I always knew the cerebellum was why practice, practice, practice improved athletic performance. Through practice, you hammer and forge muscle memory into the Purkinje neurons of the cerebellum. This is why you never forget how to ride a bike or drive a stick shift once you've learned the motor skills involved.

Cerebellum in red.

Source: Wikimedia Commons/ Life Sciences Database

The Purkinje neurons in the cerebellum play a pivotal role in orchestrating motor movements and are the seat of muscle memory. Previous research has identified that alcohol disrupts the firing pattern of cerebellar Purkinje neurons. However, the results were difficult to decipher because individual Purkinje neurons showed very different activity patterns before, during, and after the administration of alcohol.

In his recent study, Dr. Michael D. Forrest was able to use a novel mathematical model of a Purkinje neuron to show that all of this diversity and complexity can be explained by the fact that alcohol alters the firing rate of Purkinje neuron by inhibiting each neuron’s sodium-potassium pump.

Dr. Forrest and co-workers have previously shown that the sodium-potassium pump controls the intrinsic firing mode of Purkinje neurons and that the sodium-potassium pump is a computational element in the cerebellum and the brain. This is a significant breakthrough in the understanding of the role of these pumps, which were previously thought to have no direct role in brain computations.

Field Sobriety Tests Focus on Purkinje Neurons and Cerebellar Function

Alcohol causes Purkinje neurons in the cerebellum to become discombobulated which is why drunk driving is so dangerous. The statistics on drunk driving are alarming: Once every hour, someone in the United States is killed in a drunk driving car crash. Every 90 seconds, someone is injured from a drunk driving incident. Traffic accidents are the leading cause of death for teens, and roughly 1/3 of these accidents involve alcohol or another substance.

Standardized Field Sobriety Tests (SFST) are used to gauge a driver's level of impairment due to alcohol or other drug use. The three tests used to test sobriety are basically testing the Purkinje neurons of someone’s cerebellum. These tests include: Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS).

Source: Bikeriderlondon/Shutterstock

Horizontal Gaze Nystagmus (HGN) is an involuntary jerking of the eye that occurs naturally as the eyes gaze to the side. An alcohol-impaired person will often have difficulty smoothly tracking a moving object with his or her eyes. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his or her eyes.

The Walk-and-Turn test and One-Leg Stand test are "divided attention" tests that are easily performed by most unimpaired people. However, impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.

In the One-Leg Stand test, the suspect is instructed to stand with one foot approximately six inches off the ground and count aloud by thousands (One thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 30 seconds. Failing a sobriety test is directly linked to cerebellar malfunction.

Conclusion: Could a "Sobriety Pill" Reduce DUI Accidents and Deaths?

One of the most exciting aspects of Dr. Forrest's research is that it could lead to the development of a "sobreity pill." Alcohol abuse, dependence, and binge drinking are deadly. A sobriety pill that targeted the sodium-potassium Purkinje pumps could have incredible life-saving potential by reducing the motor coordination problems linked to intoxication and DUI impairments.

A sobriety pill could save lives on and off the highways. It might also help us understand the role of the cerebellum in cognitive functions and psychological disorders. Would a sobriety pill that allowed someone to pass a field sobriety test also minimize the other psychological impairments of being intoxicated? More research is needed to find these answers . . . Stay tuned!

If you'd like to read more on this topic, check out my Psychology Today blog posts:

I am looking for an answer as to why my body acts like it is drunk - staggering and fumbling - even though I haven't been drinking. I did have polio when I was a kid so I don't know if that somehow connects to the problem.